Abstract:

The objectives of this study were 1) to scale photosynthesis from leaf to crown and to tree
scale, 2) to determine the proportion of assimilated carbon used for wood construction and
whether the fraction of assimilation used for production varies among social classes and 3)
to validate the approach by comparing assimilation estimates with independent measurements
provided by the eddy covariance technique (EC). Measurements (growth and gas exchange) were
performed in a 30-year-old Fagus sylvatica stand during the 1997 growing season on
five sample trees of different crown classes (dominant, codominant and intermediate trees). A
nonlinear relationship between net CO2 assimilation and photosynthetically active radiation
(PAR) was found for each sample trees. Canopy net CO2 assimilation was then modelled over a
period of non limiting soil water soil water content. Simulated gross assimilation scaled to
stand level was in good agreement with stand measurements performed by EC.